Fuel cells have been identified as a relatively clean and efficient source of electrical power. Alkaline fuel cells are of particular interest because they operate at relatively low temperatures and have a high theoretical efficiency compared to other fuel cell technologies. Acidic fuel cells and fuel cells employing other aqueous electrolytes are also of interest. Such fuel cells operate at a voltage of usually less than one volt (typically 0.5-0.9 V). To achieve higher voltages, fuel cells are typically arranged electrically in series to form a fuel cell stack. Fuel cells employing a liquid electrolyte typically comprise an electrolyte chamber that is separated from a fuel gas chamber (containing a fuel gas, typically hydrogen) and a further gas chamber (containing an oxidant gas, usually air). The electrolyte chamber is separated from the gas chambers using electrodes that are gas permeable, and carry a catalyst such as platinum. Within a fuel cell stack the electrolyte may be circulated through the electrolyte chambers from headers or distribution ducts, so that the electrolyte flows through all the cells in parallel.
A problem with such an arrangement is that there will be some electrical (i.e. ionic) leakage current between the cells through the electrolyte in the headers or distribution ducts. This can be minimised by designing the electrolyte flow paths to raise their ionic resistance, but this measure cannot eliminate the ionic leakage currents altogether. Another problem with such fuel cell stacks is to design the cells to ensure uniformity of pressure and mass flow rates between the cells and within every cell.
WO 2011/141727 (AFC Energy) has described a fuel cell stack in which electrolyte is fed to each cell through several headers in parallel; and in which electrolyte emerges from each cell into an open channel at the top of the cell, and then trickles or falls over the edge of the stack. However this arrangement does not eliminate the ionic leakage currents; and the exposed electrolyte may cause corrosion, for example of electrical contacts.